July 10, 2019

expert reaction to effects of climate change on cities

Research. published in PLOS One, reports predicted changes that major world cities will undergo as a result of climate change.

Prof Gabi Hegerl FRS, Professor of Climate System Science at the University of Edinburgh, said:

“What I find most striking are the number of cities that move to unknown climatic conditions, most of them in the tropics. Some of these are large and fast-growing cities, and the new conditions could be harmful or dangerous as they are presently inexperienced in coming with extreme events.

“The study considers some aspects of extremes but doesn’t capture individual events like unprecedented heatwaves, droughts and heavy rainfall or flooding. Also, sea level rise will add to the difficulties faced by many of these cities.

“While this city pairing exercise is novel and interesting to do, it doesn’t quite capture the difficulties we will face.”

Prof Mike Lockwood FRS, Professor of Space Environment Physics at the University of Reading, said:

“This is a really useful piece of work on climate change visualization – but I do also have a concern that it may invite some to overlook the huge infrastructure issues that will be caused by changes to the climates of our cities.

“For example, bringing Barcelona’s climate to London sounds like it could be a good thing (if you don’t suffer from asthma or have a heart condition, that is) – except London clay shrinks and is brittle if it gets too dry and then swells and expands when very wet.  The greater swings in ground moisture expected in a warmer world would cause massive subsidence problems.  As ever, there is destructive and unforeseen devil in the details of climate change.”

Prof Richard Betts, Head of Climate Impacts Research at the Met Office Hadley Centre and Chair in Climate Impacts, University of Exeter, said:

“This study helps to put climate change in the context of human experience – and more importantly, shows that many places will see entirely new climates that are outside of current human experience.  

“Phrases like ‘London will be like Barcelona’ imply that some cities will need to adapt to the kinds of climate that many people already live in, but others like ‘Singapore will be beyond anything we currently experience’ shows that many cities will be entering unknown climate territory, especially in the tropics. 

“Without the benefit of knowing that the new climate conditions are already liveable somewhere in the world, it is harder to know whether people will be able to adapt and stay in these cities, or whether they will eventually look to move elsewhere.”

Prof Rob Wilby, Professor of Hydroclimatology at Loughborough University, said:

“Comparing the current and future background climate of global cities is an appealing communication tool. But we should also recognize that cities make their own climates depending on urban form, building materials, artificial heat sources and amount of water features and green space.

“The population density of the London Metro Region is about one tenth of Barcelona; partly because London has so much open and green space. Such differences make like-for-like comparisons problematic if we want to predict the climate conditions that people could actually experience on the ground. Moreover, there are significant variations in microclimate within large cities like London too.”

Dr Friederike Otto, Deputy Director of the Environmental Change Institute, University of Oxford, said:

“This paper provides a powerful way of illustrating what climate change could mean in reality, but it should be taken as an illustration only, not as a prediction. They aggregate over many variables and do not address model uncertainty systematically, so London would be well served to think about how they would cope with a Barcelona summer drought.

“It is a useful way to start thinking outside the box, but it does not show London’s future. Based on this it could well be that rainfall in winter changes in London in the opposite way to Barcelona.”

Dr Grant Allen, Atmospheric physicist at the University of Manchester, said:

“This research provides an exciting and useful comparative context but other important messages should not be missed. Some might wrongly think a Barcelona climate in London would be great! But this misses the point that the probability of extreme weather events is increasing as climate change progresses. What were once 1 in 100 year events a few decades ago are now becoming much more common, especially where intense rainfall is concerned in the UK. This paper looks at the shift in general climate derived from climate models. Climate models cannot capture the probability of short-term weather extremes that lead to impacts from heat waves, intense rainfall and flooding etc.

“While the mean climate may well become much like Barcelona, which presents its own chronic challenges for UK ecosystems and infrastructure, the science concerning the changing chances of extreme weather events is much less certain and recent evidence is a cause for alarm. The biggest acute human impacts from climate change may well be expected to be associated with extreme weather events while this study examines mean climate.

“The study also assumes an ambitious emissions reduction scenario, which requires enormous international effort and greater success than seen to date. We should be very careful what we may wish for – a mean climate like Barcelona is not a good thing for London or the UK.”

Prof Andrew Challinor, Professor of Climate Impacts at the University of Leeds, said:

“This clever analysis provides a simple indication of what the future holds. However, recent trends in extreme and unusual weather also tell us about the future. If I had to bet on one of these two as a means of knowing what is to come, it would be the latter.”

Dr Radhika Khosla, Senior Researcher at the Smith School of Enterprise and the Environment, University of Oxford, and Principal Investigator for the Future of Cooling Programme, Oxford Martin School, said:

“This paper provides a compelling illustration of complex climate data. Its key conclusion – that many cities will become hotter – reinforces the urgent need for mitigation against the unprecedented increase in energy demand from air conditioning, which is estimated to triple by 2050. It is vital that we avoid a feedback loop whereby the growing cooling energy needs required to maintain quality of life in urban centres in turn causes more CO2 emissions and contributes to further climate change.”

‘Understanding climate change from a global analysis of city analogues’ by Jean-Francois Bastin et al. was published in PLOS One at 7pm UK TIME on Wednesday 10 July 2019

DOI: 10.1371/journal.pone.0217592

Declared interests

None received.